1. Field of the Invention
The present invention relates to a vibration wave detector for detecting the characteristics of the vibration waves, such as an example of sound waves, to be propagated in a medium.
2. Description of the Prior Art
In the conventional system tor executing speech recognition, vibrations of a microphone which received speech signals are converted-amplified into electric signals by an amplifier, and then, the analog signals are converted into digital signals by an A/D convertor to obtain speech digital signals. Fast Fourier transform is applied to the speech digital signals by a software on a computer, so as to extract the features of the speech. Such a speech recognition system as described above is disclosed in IEEE Signal Processing Magazine, Vol. 13, No. 5, pp. 45-57 (1996).
In order to extract the features of the speech signals with better efficiency, it is necessary to calculate acoustic spectra within a time period when the speech signals are considered stationary. The speech signal is normally considered stationary within the time period of 10 through 20 msec. Therefore, signal processing such as Fast Fourier transform or the like is conducted, by the software on the computer, on the speech digital signals included within the time period with 10 through 20 msec as a period.
In the conventional speech recognizing method as described above, the speech signals including the entire instantaneous zones are converted into electric signals by a microphone. To analyze the spectra of the electric signals, the A/D conversion makes the frequencies digital. The speech digital signal data are compared with the predetermined speech wave data to extract the features of the speech.
Auditory mechanism and sound psychological physical properties are described in detail by Ohm Company Co., 1992 1, in xe2x80x9cNeuro Science and Technology Series Speech Auditory and Neuro Circuit Network Modelxe2x80x9d (pp.116-125) written by Seiichi Nakagawa, Kiyohiro Shikano, Youichi Toukura under the supervision of Shunichi Amari. This literature shows that the measure of the sound pitch audible by human beings corresponds linearly to the measure of a mel scale, instead of corresponding to linearly to frequency as physical value. The mel scale, a psychological attribute (psychological measure) representing the pitch of the sound indicated by a scale, is a scale where the intervals of the frequencies called pitches can be heard equal in interval by human beings are directly numerated. The pitch of the sound of 1000 Hz, 40 phon is defined 1000 mel. An acoustic signal of 500 mel can be heard as a sound of 0.5 time pitch. An acoustic signal of 2000 mel can be heard as the sound of twice pitches. The mel scale can be approximated as in the following (1) equation by using the frequency f [Hz] as the physical value. Also, the relationship between the sound pitch [mel] and the frequency [Hz] in the approximate equation is shown in FIG. 1.
mel=(1000/log2)log(f/1000+1)xe2x80x83xe2x80x83(1) 
In order to extract the features of the speech with better efficiency, it is often conducted to convert the frequency bands of the acoustic spectra into such mel scales. The conversion, into the mel scale, of the acoustic spectra is normally carried out by the software on the computer as in the analysis of the spectra.
Also, as a method of extracting the features of the speech with better efficiency, it is often conducted to convert the frequency bands of the acoustic spectra into a Bark scale. The Bark scale is a measure corresponding to the loudness of the psychological sound of the human being. In sounds of a certain degree or larger, the Bark scale shows the frequency band width (is called critical band width) audible by human beings, and sounds within the critical band width, even if they are different, can be heard the same. When, for example, large noises occur within the critical hand width, the scale showing the frequency band wherein the signal sounds and its noises, despite different frequencies, cannot be judged with human auditory system, is the Bark scale.
In a field of the speech signal processing, the critical band width to handle easily on the computer is demanded, and consequently the frequency axis of the acoustic spectra is shown in a Bark scale where one critical hand is defined as to one Bark. FIG. 2 shows the numerical value relationship between the critical hand width and the Bark scale. The critical band width and the Bark scale can be approximated as in the following (2) and (3) equations, using the frequency f [kHz] as a physical value.
Critical Band Width: CB[Hz]=25+75(1+1.4f2)0.69 xe2x80x83xe2x80x83(2) 
Bark Scale: B[Bark]=13 tanxe2x88x921 (0.76f)+3.5 tanxe2x88x921 (f/7.5) xe2x80x83xe2x80x83(3) 
It is known to use an engineering functional model of acoustic peripheral system in the speech recognition field, and the conception of the model is described in detail in the Literature xe2x80x9cNeuro Science and Technology Series Speech Auditory and Neuro Circuit Network Modelxe2x80x9d (pp.162-171). In the engineering functional model, frequency spectra analysis is preprocessed by band width filter groups. In, for example, the preprocessing at a Seneff model which is one of the representative engineering functional model, the frequency spectra analysis is conduced by critical band width filter groups having forty independent channels in the frequency range of 130 through 6400 Hz. At that time, the frequency band of the acoustic spectra is converted into the Bark scale.
The conversion into the Bark scale can be normally conducted by the software on the computer as in the other analysis of the spectra.
In the conventional method of conducting Fast Fourier transform on the digital acoustic signal, by the software on the computer, to analyze the spectra of the acoustic signal, the calculation amount becomes immense so that the calculating load becomes bigger.
In the conventional methods, there are not problems in the speech where the acoustic spectra does not change as time passes, like only vowel sounds. But a language is made up of consonant sounds and vowel sounds. When a consonant sound comes for a first time, and a vowel sound comes for a second time like Japanese, in general, the stress of the vowel sound becomes larger as time passes. And English is made up of complicated consonant sounds and vowel sounds.
In these cases, conventionally, it was difficult to judge when the sounds were changed from consonant sounds to the vowel sounds, because the speech was recorded instantaneously, the acoustic spectra of the entire hand were integrated through division for each constant time for analyzing of the speech. Therefore, the judging ratio of the speech recognition was reduced. In order to solve the problems, much more speech patterns are stored in advance in the computer and are applied into either of these speech patterns, thereby increasing calculation load more.
One object of the present invention is to provide a vibration wave detector which is capable of quickly and correctly conducting the frequency spectra analysis of the vibration waves on one hardware.
Other object of this invention is to provide a vibration wave detector which is capable of conducting the precise frequency spectra analysis from the high frequency side to the low frequency side.
Still other object of this invention is to provide a sound wave detector apparatus which is capable of quickly and correctly conducting the acoustic signal detection and the frequency spectra analysis on one hardware.
A vibration detector of this invention comprises a first diaphragm for receiving vibration waves to be propagated in a medium, a resonant unit having a plurality of cantilever resonators each having such a length as to resonate at an individual predetermined frequency, a retaining rod for retaining the resonant unit, a second diaphragm positioned on the opposite side of the first diagram with respect to the retaining rod, and a vibration intensity detector for detecting the vibration intensity, for each predetermined frequency, of each of the resonators.
In the above described configuration, a plurality of resonators are positioned so that resonant frequencies become sequentially lower from the first diaphragm side to the second diaphragm side.
Other vibration wave detector of this invention comprises a diaphragm for receiving vibration waves to be propagated in a medium, a resonant unit having a plurality of cantilever resonators each having such a length as to resonate at an individual predetermined frequency, a retaining rod for retaining the resonant unit, and a vibration intensity detector for detecting the vibration intensity, for each predetermined frequency, of each of the resonators, the plurality of resonators being positioned so that the resonant frequencies become sequentially lower from the near position side of the diaphragm to the far position side thereof.
In the vibration wave detector of this invention having such a configuration, the width of the retaining rod becomes narrower as it becomes further away from the first diaphragm.
The vibration wave detector of this invention has a plurality of resonators each being different in length to resonate at the predetermined frequency, transmits the vibration waves, such as sound waves, propagated in the medium to these resonators through the first diaphragm and the retaining rod, and detects the vibrations at the resonators by the vibration intensity detector. The vibration waves propagated in the medium are received by the first diaphragm, the vibration waves propagate into the retaining rod, the energy of a predetermined frequency component of the propagated vibration waves is absorbed by the cantilever resonator whose resonant frequency is almost equal to the predetermined frequency component, whereby the resonator resonates. Thus, the vibrations in the resonators are detected so that the level of each predetermined frequency component of the vibration waves propagated in the medium can be detected.
When the vibration waves are inputted without the second diaphragm, the resonant amplitude of the resonator close to the tip end (the opposite side of the input side) of the retaining rod is lowered as compared with the other resonators and the sensitivity is often lowered. When the second diaphragm is provided, resonant amplitudes of all resonators are approximately equal. On further investigation, when the inputted sound waves are provided only within the frequency hand of each resonator, it is often found out that characteristics about accuracy of resonant amplitude and sensitivity even in the absence of the second diaphragm are almost equal to those in the existence of the second diaphragm. This facts indicates that all the predetermined frequency components of the sound waves inputted from the first diaphragm are not always absorbed in a plurality of resonators. Namely, the frequency components which are not absorbed without corresponding to the resonant conditions are propagated up to the tip end (the opposite side of the input side) of the retaining rod and are reflected there. As the result, the reflected frequency components become noises, thereby to deteriorate the detection characteristic. For example, when the sounds (for example, heavy, low sounds) outside the frequency bands of a plurality of resonators are inputted, reflections occur, because of absence of a portion for absorbing energy of the frequency components, and waves interfere with each resonator, whereby noises become larger. In this invention, the second diaphragm is provided in the tip end of the retaining rod to control the reflection, whereby the unnecessary frequency components which have been propagated to the retaining rod are absorbed by the second diaphragm. In order to reduce the noises and detect the level of each frequency component precisely, resonant amplitudes from the resonators close to the input side to the far resonators are able to be make almost equal, the sensitivity on the wide frequency band is improved, and the reflections of the wave sounds outside the frequency band of the resonators are prevented. Also, stress in the end portion of the retaining rod can be relieved by attaching the first and the second diaphragms at the ends portions of the retaining rod.
In a vibration wave detector wherein the first diaphragm is made an input terminal of the vibration waves and the second diaphragm is made the absorbing end of the vibration waves, after the level detecting tests of the frequency components are repeated, it is found out that vibration energy is not propagated with better efficiency without inputting the sound waves from the high frequency side about a plurality of resonators, and the vibration energy is hardly propagated when the sound waves from the low frequency side are inputted. Namely, when the vibration waves are inputted from the high frequency side, the vibration energy is sequentially absorbed with better efficiency in each of the resonators. But when the vibration waves are inputted from the low frequency side, the vibration energy is not propagated up to an resonator corresponding to higher resonant frequency, so that the levels of higher frequency components cannot be detected precisely. In the vibration wave detector of this invention, a resonator corresponding to each higher resonant frequency is positioned on the side of the first diaphragm and a resonator corresponding to each lower resonant frequency is positioned on the side of the second diaphragm, namely, a resonator is positioned so that a resonant frequency tends to rise toward the first diaphragm side, or toward the inputting terminal of the vibration. By positioning a plurality of resonators in this way, precise detection results can be obtained about all the components from the high frequency component to the low frequency component.
When a retaining rod where the vibration waves are propagated from the first diaphragm is constant in width, the vibration energy is not propagated with better efficiency. In the vibration wave detector of this invention, the width of the retaining rod becomes gradually narrower as it goes far away from the first diaphragm side which is an input side. Since the vibration energy is propagated with better efficiency to a plurality of resonators by such a constitution of the retaining rod, the precise detection results can be obtained.
In the sound wave detector of this invention where the vibration waves are sound waves, the acoustic spectra can be obtained at real time without analytic processing, because the intensity of the sound can be detected for each of the desired frequencies. As compared with the conventional system of inputting the acoustic signals of the entire band to electrically filter to each frequency band, the present invention of mechanically analyzing the acoustic signals in this way for each of the frequencies becomes faster in processing, because the electric filtering is unnecessary.